scholarly journals Paracellular shunt ultrastructure and changes in fluid transport in Necturus proximal tubule

1983 ◽  
Vol 24 (5) ◽  
pp. 610-619 ◽  
Author(s):  
Arvid B. Maunsbach ◽  
Emile L. Boulpaep
Keyword(s):  
Proximal Tubule ◽  
Fluid Transport ◽  
Paracellular Shunt ◽  
Necturus Proximal Tubule

Nonelectrolyte permeability of the paracellular pathway in Necturus proximal tubule

1975 ◽  
Vol 228 (2) ◽  
pp. 581-595 ◽  
Author(s):  
CA Berry ◽  
EL Boulpaep
Keyword(s):  
Tight Junction ◽  
Proximal Tubule ◽  
Water Flow ◽  
Volume Flow ◽  
Osmotic Gradient ◽  
Osmotic Water ◽  
Net Flux ◽  
Gradient Measurements ◽  
Paracellular Shunt ◽  
Necturus Proximal Tubule

Micropuncture experiments were performed on Necturus proximal tubule using stationary microperfusion and microrecollection techniques. The transepithelial movement of the extracellular marker, sucrose, was used to investigate the passive permeability of the paracellular shunt pathway under steady-state conditions, during spontaneous reabsorption and water flow induced by an external osmotic gradient. Measurements were made of the sucrose permeability (P-s) efflux, net flux, and of net volume flow. True P-s determined in the absence of net volume flow and transepithelial gradient was 0.96 10-6 cm s-1. Both ouabain and isotonic volume expansion decreased shunt P-s. During reabsorption, solute-coupled water flow increased apparent P-s and net sucrose flux equalled efflux. Osmotic water flow from lumen to plasma decreased apparent P-s, with net sucrose flux equal to efflux; whereas osmotic flow from plasma to lumen increased apparent P-s but no net flux was observed. It is concluded that changes in P-s can be interpreted as relative alterations of the tight junction and the lateral spaces and that a portion of the volume flow from lumen to plasma proceeds via the tight junction.

Dependence of ion fluxes on fluid transport by rat proximal tubule

1986 ◽  
Vol 250 (4) ◽  
pp. F680-F689 ◽  
Author(s):  
K. Bomsztyk ◽  
F. S. Wright
Keyword(s):  
Proximal Tubule ◽  
Fluid Transport ◽  
Rat Kidney ◽  
Water Flux ◽  
Fluid Secretion ◽  
Proximal Convoluted Tubule ◽  
Ion Fluxes ◽  
Fluid Absorption ◽  
Fluid Flux ◽  
K Transport

The effects of changes in transepithelial water flux (Jv) on sodium, chloride, calcium, and potassium transport by the proximal convoluted tubule were examined by applying a microperfusion technique to surface segments in kidneys of anesthetized rats. Perfusion solutions were prepared with ion concentrations similar to those in fluid normally present in the later parts of the proximal tubule. Osmolality of the perfusate was adjusted with mannitol. With no mannitol in the perfusates, net fluid absorption was observed. Addition of increasing amounts of mannitol first reduced Jv to zero and then reversed net fluid flux. At the maximal rates of fluid absorption, net absorption of Na, Cl, Ca, and K was observed. When Jv was reduced to zero, Na, Cl, and Ca absorption were reduced and K entered the lumen. Na, Cl, and Ca secretion occurred in association with the highest rates of net fluid secretion. The lumen-positive transepithelial potential progressively increased as the net fluid flux was reduced to zero and then reversed. The results demonstrate that changes in net water flux can affect Na, Cl, Ca, and K transport by the proximal convoluted tubule of the rat kidney. These changes in net ion fluxes are not entirely accounted for by changes in bulk-phase transepithelial electrochemical gradients.

Stimulation of phosphate transport in the proximal tubule by metabolic substrates

1984 ◽  
Vol 247 (4) ◽  
pp. F582-F587 ◽  
Author(s):  
S. R. Gullans ◽  
P. C. Brazy ◽  
L. J. Mandel ◽  
V. W. Dennis
Keyword(s):  
Proximal Tubule ◽  
Fluid Transport ◽  
Initial Rate ◽  
Tricarboxylic Acid Cycle ◽  
Phosphate Transport ◽  
Glucose Absorption ◽  
Metabolic Substrates ◽  
Tricarboxylic Acid Cycle Intermediates ◽  
Stimulation Of

Studies of phosphate transport in the proximal tubule have recently focused on interactions with cellular metabolism. The present studies demonstrate that two fatty acids, valerate and butyrate, and two tricarboxylic acid cycle intermediates, succinate and malate, stimulate net phosphate transport in the rabbit proximal tubule by 34-117%. Valerate had no effect on the total uptake of inorganic [32P]phosphate into suspensions of proximal tubules but did enhance the initial rate of influx. Net fluid transport was unaffected by these substrates although glucose absorption increased by 10-15% following the addition of either valerate or succinate. Since valerate, butyrate, and succinate are known to stimulate gluconeogenesis and respiration, we evaluated the role of gluconeogenesis in the stimulation of phosphate transport. The addition of 3-mercaptopicolinate (1 mM), an inhibitor of gluconeogenesis, did not alter phosphate transport, nor did it prevent the valerate-induced stimulation of phosphate transport. We conclude that valerate, butyrate, succinate, and malate enhance phosphate transport by the proximal convoluted tubule. This action appears to be unrelated to effects on gluconeogenesis and may be related to close links between phosphate transport and oxidative metabolism.

scholarly journals Organic substrate effects on and heterogeneity of Necturus proximal tubule function

1980 ◽  
Vol 17 (4) ◽  
pp. 479-490 ◽  
Author(s):  
Jameson Forster ◽  
Paul S. Steels ◽  
Emile L. Boulpaep
Keyword(s):  
Proximal Tubule ◽  
Organic Substrate ◽  
Substrate Effects ◽  
Necturus Proximal Tubule

Dissociation of proximal tubular glucose and Na+ reabsorption by amphotericin B

1979 ◽  
Vol 236 (4) ◽  
pp. F392-F397
Author(s):  
P. S. Aronson ◽  
J. P. Hayslett ◽  
M. Kashgarian
Keyword(s):  
Proximal Tubule ◽  
Glucose Uptake ◽  
Amphotericin B ◽  
Membrane Vesicle ◽  
Membrane Vesicles ◽  
Na Transport ◽  
Glucose Reabsorption ◽  
Tubular Lumen ◽  
Proximal Tubular ◽  
Necturus Proximal Tubule

The effect of amphotericin B on glucose and Na+ transport was studied in the Necturus proximal tubule and in microvillus membrane vesicles isolated from the rabbit renal cortex. In the Necturus experiments, the rate constants for disappearance of radiolabeled glucose (kG) and mannitol (kM) from the tubular lumen were determined by stop-flow microperfusion. Saturability and Na+-dependence of glucose reabsorption was confirmed, since kG was reduced by raising intratubular glucose from 1 to 5 mM or by replacing intratubular Na+ with choline. Neither maneuver affected kM. Intratubular amphotericin B (10 microgram/ml), previously shown to stimulate active Na+ reabsorption in the Necturus proximal tubule, inhibited kG with no effect on kM. In the membrane vesicle preparation, amphotericin inhibited the uphill glucose uptake which results from imposing a NaCl gradient from outside to inside, but had no effect on glucose uptake in either the absence of Na+ or in the presence of Na+ when there was no Na+ gradient. Amphotericin B stimulated the uptake of Na+ by the vesicles. The observed dissociation of glucose and Na+ transport by amphotericin B is consistent with the concept that proximal tubular glucose reabsorption is energized by the luminal membrane Na+ gradient and is not directly linked to active Na+ transport per se.

Increased fluid absorption and cell volume in isolated rabbit proximal straight tubules after in vivo DOCA administration

1981 ◽  
Vol 241 (5) ◽  
pp. F502-F508 ◽  
Author(s):  
M. A. Knepper ◽  
M. B. Burg
Keyword(s):  
Proximal Tubule ◽  
Cell Volume ◽  
Fluid Transport ◽  
Sodium Intake ◽  
Plasma Concentrations ◽  
Dietary Sodium ◽  
Fluid Absorption ◽  
Direct Stimulation ◽  
Stimulation Of

To investigate whether mineralocorticoids affect the intrinsic capacity of the proximal tubule to absorb sodium and fluid, rabbits were chronically treated a number of ways to systematically vary plasma concentrations of mineralocorticoid hormones. The rate of fluid absorption and tubule dimensions were measured in superficial S2 segments from these rabbits. Chronic administration of deoxycorticosterone acetate (DOCA) was associated with a 67% increase in fluid absorption and a 29% increase in cell volume per unit tubule length. However, neither adrenalectomy nor low sodium diet significantly affected either fluid absorption or cell volume. Furthermore, marked dietary sodium restriction prevented the response to DOCA. We conclude that the DOCA-induced increases in fluid absorption and cell volume do not result from a direct stimulation of the proximal tubular cells by the steroid but more likely are responses to systemic effects of DOCA administration that are dependent on the level of sodium intake. Thus, we find no evidence for a direct mineralocorticoid stimulation of sodium and fluid transport by the S2 portion of the proximal tubule.

Electrophysiology of salamander proximal tubule. II. Interspace NaCl concentrations and solute-coupled water transport

1986 ◽  
Vol 251 (2) ◽  
pp. F334-F347
Author(s):  
H. Sackin
Keyword(s):  
Low Temperature ◽  
Proximal Tubule ◽  
Water Transport ◽  
Time Course ◽  
Fluid Transport ◽  
Bath Temperature ◽  
Null Point ◽  
Constant Composition ◽  
Nacl Concentration ◽  
Test Concentration

The role of the paracellular interspace in solute-coupled water transport was investigated in isolated perfused salamander (Ambystoma) proximal tubules using a null-point technique to estimate interspace NaCl concentrations. Constant composition of luminal fluid was maintained by rapid (200 nl/min) perfusion of tubules 600,micron or less in length. Inhibition of active transport by a decrease in bath temperature from 22 to 0 degrees C in 400 ms produced rapid depolarizations of both the transepithelial (Vte) and basolateral (Vbl) potential, followed by slower changes in potential that occurred at low temperature. During this period, the time course of Vbl was independent of small changes in bath NaCl concentration, whereas the time course of Vte at low temperature varied from a slow depolarization to a slow repolarization depending on whether the concentration of NaCl in the bath equaled or exceeded that in the perfusate. Absence of a slow change in Vte at low temperature indicated a match between the NaCl concentration of the interspace and the test concentration of NaCl in the bath. Using this technique with 12 tubules, the normal interspace NaCl concentration appeared to be approximately 4% above the NaCl concentration of either the lumen or bath, demonstrating that the interspace of the salamander proximal tubule can function as a local hyperosmotic compartment to facilitate fluid transport between solutions of identical composition.

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